The polyester resin has been widely used in fields of the packing materials, the forming products and the films, and is one of the environment-friendly plastics which has no endocrine disruptors. Recently, in the polycarbonate which has been used as the heat-resisting container for food, harmfulness of bisphenol-A to the human being has been revealed. So, the demand for the environment-friendly transparent and heat-resisting polyester resin has more increased. The polyerster resin which is copolymerized with at least two glycol or dicarboxylic acid components has been com-mercially widely used to improve a moldability thereof and to remove a crystallinity thereof. In the case of homopolyester which is polymerized with only terephthalic acid and ethyleneglycol, material properties and heat-resistance thereof can be enhanced through a stretching-induced crystallization and heat-setting. However, there are lim-itations on application and enhancement of heat-resistance. In the case of polyester which is copolymerized with at least two glycol or terephthalic acid components, there is a disadvantage that it is difficult to enhance heat-resistance thereof by stretching or crystallize process. As another method to enhance heat-resistance of the polyester, it is known that the isosorbide which is an environment-friendly diol compound derived from starch and represented by following Formula 1, is used as one of monomers.

According to the results of past studies, isosorbide has low activity as a secondary alcohol so that it is difficult to prepare high viscous polyester which can be used for manufacturing sheets or bottles. However, recent U.S. Pat. No. 5,959,066 discloses a method for preparing polyester having the intrinsic viscosity of more than 0.35 dl/g by melt polymerization using terephthalic acid or dimethylterephthalate and various diols comprising isosorbide. The polyester resin having the intrinsic viscosity of more than 0.35 dl/g is used for optical products and coating, and the polyester resin having the intrinsic viscosity of more than 0.4 dl/g is used for CD, and the polyester resin having the intrinsic viscosity of more than 0.5 dl/g can be used for a bottle, a film, a sheet and injection molding. Moreover, U.S. Pat. No. 6,063,464 discloses a method for preparing the polyester having the intrinsic viscosity of more than 0.15 dl/g by melt polymerization using the glycol components comprising isosorbide. The above patents disclose a method for polymerizing polyester using common catalysts with all of acids and diols comprising isosorbide, however, it seems that a composition for higher impact strength is needed to be used for normal plastics. As shown in Examples of U.S. Pat. No. 6,063,464, notch izod impact strength of products produced by adding glass fiber of 29.6% to polyesters comprising isosorbide of 3, 6, and 13%, shows the range of 43-116 Jim according to the amount of isosorbide, however, impact strength of a product without glass fiber is not mentioned. If glass fiber is added, usually impact strength is enhanced, but transparency is extremely lowered and applications are limited due to the harmfulness of glass fiber.